RF switch with bypass topology

ABSTRACT

An RF signal switch circuit that allows connection of any of N radio frequency (RF) input terminals to a switch output port, either in a low loss mode, in a bypass mode, or, optionally, in a signal function mode. Embodiments of the invention allow for both a single switch in the series input path to a target circuit while still having the ability to isolate the bypass path from the target circuit. In the low loss and bypass mode, the circuit simultaneously exhibits low input insertion loss (and thus a low noise factor) and high bypass mode isolation.

CROSS-REFERENCE TO RELATED APPLICATIONS—CLAIMS OF PRIORITY

The present application is a continuation of, and claims priority to,like-named co-pending and commonly assigned U.S. patent application Ser.No. 17/244,162, filed Apr. 29, 2021, to issue on Aug. 16, 2022 as U.S.Pat. No. 11,418,186, which is a continuation of, and claims priority to,like-named co-pending and commonly assigned U.S. patent application Ser.No. 16/885,140, filed May 27, 2020, issued on May 4, 2021 as U.S. Pat.No. 10,998,901, which is a continuation of, and claims priority to,like-named and commonly assigned U.S. patent application Ser. No.16/250,858, filed Jan. 17, 2019 (now U.S. Pat. No. 10,700,679 issuedJun. 30, 2020), which is a continuation of, and claims priority to,like-named and commonly assigned U.S. patent application Ser. No.16/017,907, filed Jun. 25, 2018 (now U.S. Pat. No. 10,291,223, issuedMay 14, 2019), which is a continuation-in-part of, and claims priorityto, like-named and commonly assigned U.S. patent application Ser. No.15/698,088, filed Sep. 7, 2017 (now abandoned), which is a continuationof U.S. patent application Ser. No. 15/426,848, filed Feb. 7, 2017 (nowU.S. Pat. No. 9,800,238, issued Oct. 24, 2017), which is a continuationof U.S. patent application Ser. No. 14/811,159, filed Jul. 28, 2015 (nowU.S. Pat. No. 9,602,098, issued Mar. 21, 2017), the contents of all ofwhich are hereby incorporated by reference.

BACKGROUND (1) Technical Field

This invention relates to electronic radio frequency (RF) circuits, andmore particularly to RF signal switching circuits.

(2) Background

Radio frequency (RF) signal switches are common circuits for routing RFsignals between various parts of an RF system, such as between one ormore antennas and one or more transmitter and/or receiver circuits. Forexample, RF signal switches are used in such devices as one-way andtwo-way radios, including cellular telephones, and in global positioningsystem (GPS) devices.

It is fairly common to use RF signal switches in electronic systems thatare sensitive to noise, such as radio signal receivers. Such receiversare often presented with very weak signals (for example, transmittedradio waves captured by an antenna), and accordingly, it is common touse a low-noise amplifier (LNA) to amplify such signals. It is alsocommon to provide a matching network at the input of the LNA to maximizepower transfer to the LNA.

The noise figure (NF) of a low noise amplifier (LNA) is very sensitiveto the impedance presented and the insertion loss (IL) in front of theinput to the LNA. For example, in a typical cellular radio LNAconfiguration, a set of bandpass filters in series with an RF switchexist at the input of the LNA and are used to select a specific band tobe presented to a radio transceiver. In order to reduce the NF, RFsignal switches with low insertion loss (IL) are required. However, insome modes of operation, the LNA must be bypassable, and in such a mode,the LNA should be isolated from the bypass signal path.

For example, FIG. 1 is a schematic diagram of a prior art RF signalswitch 100 in which one of N RF input terminals RF₁-RF_(N) may beconnected to a Switch Output port, either through a matching network andLNA block 102 or through a bypass path 104. The RF input terminalsRF₁-RF_(N) may be connected to respective antennas; the matching networkand LNA block 102 are generally external to the RF signal switch 100, asindicated by the dashed lines.

In the illustrated example, in an “in-circuit” mode, the input terminalRF₁ may be connected to the matching network and LNA block 102 byclosing the corresponding series switch S₁, opening a correspondingshunt switch Sh₁, opening the Bypass Switch, closing an output connectorswitch S_(C), and opening an output connector shunt switch Sh_(C). Inthis mode, for each other RF input terminal RF₂-RF_(N), thecorresponding series switch S₂-S_(N) is open and the corresponding shuntswitch S₂-S_(N) is closed. Any other RF input terminal RF₂-RF_(N) may beconnected in-circuit to the matching network and LNA block 102 in asimilar manner.

In a bypass mode, the input terminal RF₁ may be connected directly tothe Switch Output by closing the corresponding series switch S₁, openingthe corresponding shunt switch Sh₁, closing the Bypass Switch, openingthe output connector switch S_(C), and closing the output connectorshunt switch Sh_(C). In this mode, for each other RF input terminalRF₂-RF_(N), the corresponding series switch S₂-S_(N) is open and thecorresponding shunt switch S₂-S_(N) is closed. Any other RF inputterminal RF₂-RF_(N) may be connected to bypass the matching network andLNA block 102 in a similar manner.

A problem with the circuit configuration shown in FIG. 1 is that thematching network at the input of the LNA is not isolated from the bypasspath 104 when the LNA is not active. The matching network can adverselyaffect the output impedance of the RF signal switch 100 and cause the ILof the bypass path 104 to be degraded, the severity of which isdependent on the design and component values of the LNA input matchingnetwork. This degradation of the bypass path IL causes module designersto struggle to find a balance between having a good LNA input match andmaintaining a low bypass path IL.

If it is desired to isolate the bypass path from the LNA input matchingnetwork, standard practice is to add another series/shunt switch pairbefore the matching network. For example, FIG. 2 is a schematic diagramof the prior art RF signal switch of FIG. 1 in which an isolationseries/shunt switch pair S_(I)/Sh_(I) 106 are connected before thematching network and LNA block 102. In the bypass mode, the isolationseries switch S_(I) is open and the isolation shunt switch Sh_(I) isclosed, thereby coupling the matching network input to circuit groundand completely isolating the matching network from the bypass path 104.Conversely, in the in-circuit mode, the isolation series switch S_(I) isclosed and the isolation shunt switch Sh_(I) is open.

However, a downside of the circuit configuration shown in FIG. 2 is thatthe added series switch S_(I) increases the input IL to the LNA comparedto the configuration shown in FIG. 1 , and thus increases the system NF.This is so because the illustrated switches are not perfect conductorswhen closed, but exhibit some amount of impedance.

Further, in some applications, greater flexibility with respect toswitching paths is desirable. For example, LNA circuits are becomingmore complicated, often requiring tunable gain states. For suchapplications, it would be desirable to have an option to choose a highloss signal path for the LNA input for gain tuning while maintainingboth a low loss signal path option for high gain and a low NF, and ahigh isolation bypass signal path. As another example, rather thanhaving a selectable high loss signal path, it may be desirable in someapplications to selectively apply a signal function that intentionallyalters an RF signal in a desired manner, such as by altering signalphase and/or signal amplitude (e.g., by attenuation or amplification).

Accordingly, there is a need for an RF signal switching circuit thatsimultaneously exhibits low input IL (and thus a low NF) and highisolation. There is also a need for an RF signal switching circuit thatsimultaneously provides a signal function mode, a low loss mode, and ahigh isolation bypass mode. The present invention addresses these needs.

SUMMARY OF THE INVENTION

The invention encompasses embodiments of an RF signal switch circuitthat allows connection of any of N RF input terminals RF₁-RF_(N) to aSwitch Output port, either in a low loss mode or in a bypass mode.Embodiments of the invention allow for both a single switch in theseries input path to a target circuit while still having the ability toisolate the bypass path from the target circuit. In both modes, thecircuit simultaneously exhibits low input IL (and thus a low NF) andhigh bypass mode isolation. Variant embodiments include both a low lossmode and a bypass mode, as well as a signal function mode.

In one dual-mode embodiment, an in-circuit path of the RF signal switchcircuit is coupled to the input of an isolation and/or insertion losssensitive target circuit (such as an LNA or a digital step attenuator)that may include an optional matching network. The target circuit andthe optional matching network are typically off-circuit with respect tothe RF signal switch circuit, but the entire circuit may be fabricatedas a hybrid or monolithic structure. In some embodiments, the matchingnetwork may be integrated with the target circuit.

In one dual-mode embodiment, each of the RF input terminals RF₁-RF_(N)is directly connected to three corresponding switches: an in-pathconnector switch IC_S_(x), a shunt switch Sh_(x), and a bypass switchBP_S_(x) (where “x” represents the corresponding RF input terminalidentifier, from 1 to N, and where N may be 1). For each of the RF inputterminals RF₁-RF_(N), all of the in-path connector switches IC_S_(x) andan isolation shunt switch Sh_(I) are connected to an in-circuit path. Inalternative embodiments, each of the RF input terminals RF₁-RF_(N) mayhave one or more sets of in-path connector switch IC_S_(x), andcorresponding isolation shunt switches Sh_(I) connected to parallelin-circuit paths. Such a configuration would, for example, allowmultiple antennas to be selectively coupled to multiple target circuitswithout increasing the number of series switches to any one targetcircuit. The output of the target circuit is connected to a switchreturn path, which is in turn selectively connectable to the SwitchOutput of the RF signal switch circuit through an output connectorseries switch S_(C), or to circuit ground through an output connectorshunt switch Sh_(C). In operation, an RF signal applied to any of the RFinput terminals RF₁-RF_(N) may be connected to the target circuitthrough a single switch (and then to the Switch Output), or applied to abypass path to the Switch Output with complete isolation of any matchingnetwork coupled to the switching circuit.

Three-mode embodiments of the invention that include a bypass mode, alow loss mode, and a signal function mode include an RF signal switchcircuit having at least one first type RF signal port, each first typeRF signal port having a first shunt switch coupled to the first type RFsignal port and configured to selectively couple the first type RFsignal port to circuit ground, a first series switch coupled between thefirst type RF signal port and configured to be coupled to at least onecorresponding target circuit, and at least one set of second seriesswitches coupled to the first type RF signal port; at least one firstcircuit path each coupled to a corresponding second shunt switch andcoupled to a corresponding one set of second series switches, each firstcircuit path being configured to be coupled to at least one signalfunction circuit; at least one second circuit path configured to becoupled to the at least one signal function circuit, and being coupledto a corresponding third shunt switch; at least one third series switchcoupled to a corresponding one second circuit path and to at least onefirst series switch; at least one second type RF signal port; and aswitching network coupled to the at least one second type RF signalport, the switching network including at least one first switch patheach having a series switch coupled to at least one second type RFsignal port and configured to be coupled to one corresponding targetcircuit, and a shunt switch coupled to a node between such series switchand such corresponding target circuit and configured to selectivelycouple that node to circuit ground, and at least one second switch patheach having a first series switch coupled to the at least one secondtype RF signal port, a second series switch coupled to the first seriesswitch and to at least one second circuit path, and a shunt switchcoupled to a node between the first and second series switches andconfigured to selectively couple that node to circuit ground.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a prior art RF signal switch in whichone of N RF input terminals RF₁-RF_(N) may be connected to a SwitchOutput either through a matching network and LNA block, or through abypass path.

FIG. 2 is a schematic diagram of the prior art RF signal switch of FIG.1 in which an isolation series/shunt switch pair S_(I)/Sh_(I) isconnected before the matching network and LNA block.

FIG. 3 is a schematic diagram of an embodiment of a dual-mode RF signalswitch circuit in accordance with the present invention.

FIG. 4A is a schematic diagram of the embodiment shown in FIG. 3configured in an in-circuit mode.

FIG. 4B is a schematic diagram of the embodiment shown in FIG. 3configured in a bypass mode.

FIG. 5 is a schematic diagram of a high-isolation “T” typeseries/shunt/series bypass switch replacement circuit for each of thebypass switches BP_S₁ to BP_S_(N) shown in FIG. 3 .

FIG. 6A is a graph comparing the insertion loss of the series input pathto the LNA versus frequency for each of the three simulated circuittopologies from FIG. 1 , FIG. 2 , and FIG. 3 .

FIG. 6B is a graph comparing the insertion loss of the bypass pathversus frequency for each of the three simulated circuit topologies fromFIG. 1 , FIG. 2 , and FIG. 3 .

FIG. 7 is a schematic diagram of an embodiment of a triple-mode RFsignal switch circuit in accordance with the present invention.

FIG. 8A is a schematic diagram of the embodiment shown in FIG. 7configured in a bypass mode.

FIG. 8B is a schematic diagram of the embodiment shown in FIG. 3configured in a low loss mode.

FIG. 8C is a schematic diagram of the embodiment shown in FIG. 3configured in a signal function mode.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION OF THE INVENTION Dual Mode Embodiments

FIG. 3 is a schematic diagram of an embodiment of a dual-mode RF signalswitch circuit 300 in accordance with the present invention. The RFsignal switch circuit 300 allows connection of any of N RF inputterminals RF₁-RF_(N) to a Switch Output port, either in an in-circuitmode or in a bypass mode. Embodiments of the invention allow for both asingle switch in the series input path while still having the ability toisolate the bypass path from an input matching network. In both modes,the circuit simultaneously exhibits low input IL (and thus a low NF) andhigh bypass mode isolation.

In the illustrated embodiment, an in-circuit path 302 of the RF signalswitch circuit 300 is configured to be coupled to the input of anisolation and/or insertion loss sensitive target circuit 304 (such as anLNA or a digital step attenuator) directly or through an optionalmatching network 306 (shown in dotted outline). The target circuit 304and the matching network 306 are typically off-circuit with respect tothe RF signal switch circuit 300, but the entire circuit illustrated inFIG. 3 may be fabricated as a hybrid or monolithic structure. In someembodiments, the matching network 306 may be integrated with the targetcircuit 304. However, for convenience, the description below will treatthe target circuit 304 and the matching network 306 as separateelements.

In the illustrated embodiment, each of the RF input terminals RF₁-RF_(N)is directly connected to three corresponding switches: an in-pathconnector switch IC_S_(x), a shunt switch Sh_(x), and a bypass switchBP_S_(x) (where “x” represents the corresponding RF input terminalidentifier, from 1 to N, and where N may be 1). For each of the RF inputterminals RF₁-RF_(N), all of the in-path connector switches IC_S_(x) andan isolation shunt switch Sh_(I) are connected to the in-circuit path302.

The RF signal switch includes a switch return path 308 configured to becoupled to the output of the target circuit 304. The switch return path308 is in turn selectively connectable to the Switch Output of the RFsignal switch circuit 300 through an output connector series switchS_(C), or to circuit ground through an output connector shunt switchSh_(C).

In alternative embodiments, the RF input terminals RF₁-RF_(N) may haveone or more sets of in-path connector switch IC_S_(x), and correspondingisolation shunt switches Sh_(I) connected to parallel in-circuit paths302. Such a configuration would, for example, allow multiple antennas tobe selectively coupled to multiple target circuits 304 withoutincreasing the number of series switches to any one target circuit 304.In such a configuration, the RF signal switch 300 would have parallelswitch return paths 308, each configured to be coupled to acorresponding target circuit 304, a corresponding output connectorseries switch S_(C), and a corresponding output connector shunt switchSh_(C).

All of the switches described above for FIG. 3 may be controlled byexternal switching circuitry (not shown) of conventional design to seteither open states or closed states for the switches.

FIG. 4A is a schematic diagram of the embodiment shown in FIG. 3configured in an in-circuit mode. In this example, a signal applied toRF input terminal RF₁ is coupled through the closed in-path connectorswitch IC_S₁ to the in-circuit path 302, through the matching network306 to the target circuit 304, back to the switch return path 308 andthrough the closed output connector series switch S_(C), and then to theSwitch Output. The shunt switch Sh₁ and the bypass switch BP_S₁ for theRF input terminal RF₁ are open, as are the isolation shunt switch Sh_(I)and the output connector shunt switch Sh_(C).

Each of the other RF input terminals RF₂-RF_(N) are shunted to circuitground through their corresponding shunt switch Sh₂-Sh_(N), and theircorresponding in-path connector switches IC_S₂ to IC_S_(N) and bypassswitches BP_S₂ to BP_S_(N) are open, thus isolating the RF inputterminals RF₂-RF_(N) from the active signal path through RF inputterminal RF₁.

In the configuration shown in FIG. 4A, the input signal at the RF inputterminal RF₁ passes through only one switch (IC_S₁) before being coupledto the matching network 306, thus minimizing insertion loss to thematching network 306 and target circuit 304.

FIG. 4B is a schematic diagram of the embodiment shown in FIG. 3configured in a bypass mode. In this example, a signal applied to RFinput terminal RF₁ is coupled through the closed bypass switch BP_S₁ tothe Switch Output. The shunt switch Sh₁ and the in-path connector switchIC_S₁ for the RF input terminal RF₁ are open. The isolation shunt switchSh_(I) and the output connector shunt switch Sh_(C) are both closed,thereby coupling the input to the matching network 306 and the output ofthe target circuit 304 to circuit ground.

Each of the other RF input terminals RF₂-RF_(N) are again shunted tocircuit ground through their corresponding shunt switch Sh₂-Sh_(N), andtheir corresponding in-path connector switches IC_S₂ to IC_S_(N) andbypass switches BP_S₂ to BP_S_(N) are open, thus isolating the RF inputterminals RF₂-RF_(N) from the active signal path through RF inputterminal RF₁.

In the configuration shown in FIG. 4B, the input signal at the RF inputterminal RF₁ passes through only one switch (BP_S₁) before being coupledto the Switch Output, and is completely isolated from the matchingnetwork 306 and the target circuit 304.

As should be clear, any other RF input terminal RF₂-RF_(N) may beconnected in an in-circuit mode or in a bypass mode in a similar manner.In the case of multiple target circuits 304, each inactive targetcircuit 304 would be isolated by appropriate settings of the shunt andseries switches of the corresponding in-circuit path 302 and switchreturn path 308 (for example, by opening the corresponding in-pathconnector switch IC_Sx, closing the corresponding isolation shunt switchSh_(I), opening the corresponding output connector series switch S_(C),and closing the corresponding output connector shunt switch Sh_(C)).

Alternative Bypass Switch Circuit

For the example shown in FIG. 3 , if even higher isolation of the SwitchOutput from the input of the target circuit 304 is desired, thecorresponding bypass switches BP_S₁ to BP_S_(N) may be replaced by a “T”type series/shunt/series circuit bypass switch configuration. This maybe useful to better isolate the Switch Output from the input of thetarget circuit 304, since a single bypass switch BP_S₁ (particularly oneimplemented as a field effect transistor) may behave as a capacitorcapable of passing some amplified signal frequencies present on theSwitch Output over to the input of the target circuit 304. Betterisolation will prevent feedback and increase the stability of the targetcircuit 304. However, if the target circuit 304 does not provideamplification (e.g., if the target circuit is a digital stepattenuator), then the simpler single-switch bypass switches BP_S₁ toBP_S_(N) shown in FIG. 3 may be preferred.

FIG. 5 is a schematic diagram of a high-isolation “T” typeseries/shunt/series bypass switch replacement circuit 500 for each ofthe bypass switches BP_S₁ to BP_S_(N) shown in FIG. 3 . For an activesignal path (e.g., for a signal applied to RF input terminal RF₁) in thebypass mode, series switch SwA is closed, series switch SwB is closed,and shunt switch Sh is open, thus allowing signal propagation from theRF input terminal RF₁ to the Switch Output (but with slightly worsebypass path IL because of the addition of a second series switchcompared to the single-switch bypass switches BP_S₁ to BP_S_(N) shown inFIG. 3 ).

For an active signal path in the in-circuit mode and for inactive signalpaths in either mode, series switch SwA is open, series switch SwB isopen, and shunt switch Sh is closed, thus grounding the junction betweenthe two series switches SwA, SwB and thereby significantly increasingthe isolation of the input to the target circuit 304 from the SwitchOutput.

Simulation Results

The two circuit topologies shown in FIG. 1 and FIG. 2 and the novelcircuit topology shown in FIG. 3 were simulated for comparison usingselected resistors, capacitors, inductors, and the scattering parameters(S-parameters) of a selected LNA. Since FET switches are known to behaveas capacitors when open (non-conducting) and resistors when closed(conducting), in the simulation capacitors were used to represent openswitches and resistors were used to represent closed switches. Thecapacitive and resistive values were chosen based on current RF switchIC technology. The inductors were used on the port locations to simulatean expected exterior matching network. The S-parameters were measured ona typical LNA (turned off) with an adjoining matching network that couldbe used in conjunction with such switches. This was done to introducethe effect the turned-off LNA with input matching network would have ifits input was not properly isolated from the bypass path. The bypassswitch was simulated using the high-isolation series/shunt/seriesconfiguration shown in FIG. 5 .

FIG. 6A is a graph 600 comparing frequency versus the insertion loss ofthe series input path to the LNA for each of the three simulated circuittopologies from FIG. 1 (curve 602), FIG. 2 (curve 604), and FIG. 3(curve 606). Point m2 represents a frequency of about 1.5 GHz, and pointm3 represents a frequency of about 2.69 GHz. The FIG. 1 (curve 602) andFIG. 3 (curve 606) circuit topologies have similar IL performance, butthe FIG. 2 (curve 604) circuit topology (with better isolation than theFIG. 1 circuit topology) has degraded IL due to the addition of a secondswitch in the series input path.

FIG. 6B is a graph 610 comparing frequency versus the insertion loss ofthe bypass path for each of the three simulated circuit topologies fromFIG. 1 (curve 612), FIG. 2 (curve 614), and FIG. 3 (curve 616). Point m4represents a frequency of about 1.5 GHz, and point m5 represents afrequency of about 2.69 GHz. In contrast to the FIG. 6A results, theFIG. 2 (curve 614) and FIG. 3 (curve 616) circuit topologies havesimilar IL performance, with the FIG. 3 (curve 616) circuit topologybeing a little better at all frequencies, and significantly better athigher frequencies. The adverse effect of a non-isolated LNA (turnedoff) can be seen in the bypass IL of the FIG. 1 (curve 612) circuittopology, which worsens rapidly as frequency increases. In allsimulations, the input series IL was optimized by using only an inductorfor the input matching network; the severity of the degraded IL in thebypass path is very much dependent on the type of input matching networkused. A different matching network circuitry could cause an even greateramount of IL degradation for the FIG. 1 (curve 612) circuit topology.

Comparing FIG. 6A and FIG. 6B, it is quite apparent that the novelcircuit topology shown in FIG. 3 (curves 606, 616) has better overall ILperformance than the circuit topologies of FIG. 1 (curves 602, 612) andof FIG. 2 (curves 604, 614) with their attendant tradeoff between bypassIL and input series IL.

Triple Mode Embodiments

The dual mode RF signal switch circuit 300 described above with respectto FIG. 3 provide a low loss signal path option as well as a bypass pathoption that is isolated from external circuitry (e.g., an isolationand/or insertion loss sensitive target circuit 304 such as an LNA or adigital step attenuator, directly or through an optional matchingnetwork 306). However, the RF signal switch circuit 300 is also usefulin other circuit configurations. For example, the RF signal switchcircuit 300 may be repurposed to provide a high loss signal path optionin addition to maintaining a low loss signal path option and an isolatedbypass signal path option. Providing a high loss signal path may beuseful, for example, to enable gain tuning for the input to an LNA. Asanother example, rather than having a selectable high loss signal path,it may be desirable in some applications to selectively apply a signalfunction that intentionally alters an RF signal in a desired manner,such as by selectively altering signal phase and/or signal amplitude(e.g., by attenuation or amplification).

FIG. 7 is a schematic diagram of an embodiment of a triple-mode RFsignal switch circuit 700 in accordance with the present invention. TheRF signal switch circuit 300 of FIG. 3 is carried over, and is coupledby the in-circuit path 302 to a signal function circuit 702. The signalfunction circuit 702 may be, for example, one or more of a digital stepattenuator (DSA), a digitally-controlled phase shifter, various types ofamplifiers, or other circuitry that applies a signal function thatintentionally alters an RF signal in a desired manner. A desirablecharacteristic of the signal function circuit 702 for many applicationsis that it have a selectable bypass mode that minimally alters anapplied RF signal. Some or all of the signal function circuit 702 may beimplemented as part of an integrated circuit (IC) chip that includes theRF signal switch circuit 300, or may be implemented as a separate ICand/or with some external components (e.g., large inductors orcapacitors may be off-chip).

Examples of signal function circuits are described in U.S. Pat. No.9,024,700, issued on May 5, 2015, entitled “Method and Apparatus for usein Digitally Tuning a Capacitor in an Integrated Circuit Device”; U.S.Pat. No. 9,197,194, issued on Nov. 24, 2015, entitled “Method andApparatus for Use in Tuning Reactance in a Circuit Device”; U.S. Pat.No. 9,397,635, issued on Jul. 19, 2016, entitled “Segmented Attenuatorwith Glitch Reduction”; and U.S. Pat. No. 9,531,359, issued on Dec. 27,2016, entitled “Improved Multi-State Attenuator”; all of which arehereby incorporated by reference.

A selectable signal path 704 of the RF signal switch circuit 300 iscoupled to an isolation and/or insertion loss sensitive target circuit706 that may include, for example, an LNA, an impedance matchingnetwork, and/or other circuitry. Again, some or all of the targetcircuit 706 may be implemented as part of an IC that includes the RFsignal switch circuit 300, or may be implemented as a separate IC and/orwith external components (e.g., large inductors or capacitors may beoff-chip).

The target circuit 706 may be coupled to further circuitry, such as anoptional signal function circuit 708 that provides the same or differentsignal function capability as the signal function circuit 702 (e.g., oneor more of a DSA, a digitally-controlled phase shifter, various types ofamplifiers, or other circuitry that applies a signal function thatintentionally alters an RF signal in a desired manner). In someembodiments, the signal function circuit 708 may be provided alone inlieu of the signal function circuit 702. A desirable characteristic ofthe signal function circuit 708 for many applications is that it have aninternal selectable bypass mode that minimally alters an applied RFsignal. Again, some or all of the signal function circuit 708 may beimplemented as part of an IC that includes the RF signal switch circuit300, or may be implemented as a separate IC and/or with externalcomponents.

The target circuit 706 is coupled, directly or through the signalfunction circuit 708, to a switching network 710. The signal functioncircuit 702, if present, is also coupled to the switching network 710and to the switch return path 308 (if the switching network 710 isomitted, then the RF signal switch circuit 300 is coupled by thein-circuit path 302 to the switching network 710 and the switch returnpath 308). The switching network 710 is coupled to an RF₀ port andincludes two selectable signal paths. A first switch path 712 includes aseries switch SwA coupled between the RF₀ port and a correspondingtarget circuit 706, and a corresponding shunt switch ShA coupled to anode between the series switch SwA and the corresponding target circuit706 and configured selectively couple that node to circuit ground. Asecond switch path 714 includes a first and second series switches SwB1,SwB2, and a corresponding shunt switch ShB coupled to a node between thefirst and second series switches SwB1, SwB2 and configured toselectively couple that node to circuit ground. The switching network710 may be implemented as part of an IC that includes the RF signalswitch circuit 300, and/or may be implemented as a separate IC.

While RF signal switch circuit 300 of FIG. 3 is carried over, theoperation of some of its internal switches has been changed to modify RFsignal paths to and from the RF₁-RF_(N) ports for different modes. Morespecifically, any of three signal path modes can be selected: a bypassmode, a low loss mode, or a signal function mode. To avoid confusion,the internal switches of the RF signal switch circuit 300 retain thereference labels used in FIG. 3 , even though some RF signal pathsperform different functions than in FIG. 3 , as further described below.Note also that the various ports, RF₀ and RF₁-RF_(N), are inherentlybidirectional, and thus can be coupled to other circuit elements asinput ports and/or as output ports.

FIG. 8A is a schematic diagram of the embodiment shown in FIG. 7configured in a bypass mode. In this mode, the switches of the RF signalswitch circuit 300 and of the switching network 710 are set to convey anRF signal between the RF₀ port and a selected one of the RF₁-RF_(N)ports while isolating the target circuit 706. For example, the RF₀ portmay be coupled to the RF₁ port by closing series switches SwB1, SwB2,and IC_S1, opening all other series switches (with the possibleexception of at least one bypass switch BP_S_(x), see next paragraph),opening shunt switches ShB, Sh₁, and Sh_(C), and closing all other shuntswitches. In addition, the signal function circuit 702 would be setinternally to a bypass state. In such a configuration, the targetcircuit 706 is isolated from the active bypass signal path between theRF₀ port and the RF₁ port.

The example switch configuration for coupling port RF₀ to port RF₁provides a degree of isolation for the target circuit 706. For betterisolation in the bypass mode, the bypass switch BP_S_(x) of at least oneRF port (e.g., RF₂-RF_(N)) not involved in the signal path conveying theRF signal may be closed, creating a connection to circuit ground for theselectable signal path 704 through the corresponding closed shuntswitch. Thus, for example, referring to the example in FIG. 8A, bypassswitch BP_S_(N) and shunt switch Sh_(N) may both be closed in the bypassmode to provide greater isolation for the target circuit 706.Alternatively, an extra shunt switch Sh_(x) (shown in dotted outline inFIGS. 7 and 8A-8C) may be provided between the selectable signal path704 and circuit ground. Closing the extra shunt switch Sh_(x) in thebypass mode would enable extra isolation for the target circuit 706; theextra shunt switch Sh_(x) would normally be open for all other modes.

FIG. 8B is a schematic diagram of the embodiment shown in FIG. 3configured in a low loss mode. In this mode, the switches of the RFsignal switch circuit 300 and of the switching network 710 are set toconvey an RF signal between the RF₀ port and a selected one of theRF₁-RF_(N) ports through the target circuit 706. For example, the RF₀port may be coupled to the RF₁ port through the target circuit 706 byclosing series switches SwA and BP_S₁, opening all other series switchesconnected to a path conveying an RF signal (thus, switch SwB2 may eitherbe closed, as shown in FIG. 8B, or opened, since it would not beconnected to a path conveying an RF signal because switches SwB1 and Scwould be open), opening shunt switches ShA and Sh₁, and closing allother shunt switches. In such a configuration, the target circuit 706coupled on a low loss signal path between the RF₀ port and the RF₁ port.As in the case of the low loss in-circuit mode of the dual-modeconfiguration of FIG. 4A, an RF signal need only traverse through oneinput series switch and a total of two series switches (albeit differentswitches), thus keeping insertion loss low.

FIG. 8C is a schematic diagram of the embodiment shown in FIG. 3configured in a signal function mode. In this mode, the switches of theRF signal switch circuit 300 and of the switching network 710 are set toconvey an RF signal between the RF₀ port and a selected one of theRF₁-RF_(N) ports through the target circuit 706 and through the signalfunction circuit 702. For example, the RF₀ port may be coupled to theRF₁ port through the target circuit 706 and the signal function circuit702 by closing series switches SwA, S_(C), and IC_S1, opening all otherseries switches, opening shunt switches ShA, Sh_(C), and Sh₁, andclosing all other shunt switches. In such a configuration, the targetcircuit 706 coupled on a signal path between the RF₀ port and the RF₁port through the signal function circuit 702, which may apply a desiredsignal modification function (e.g., phase shift and/or amplitudemodification, such as by attenuation or amplification).

Thus, in effect, the RF signal switch circuit 300 of FIG. 3 has beenreconfigured such that the original bypass signal paths (through theBP_Sx series switches) are repurposed as low loss signal paths, and theoriginal low loss signal paths (through the IC_Sx series switches) arerepurposed as signal function (e.g., high loss) signal paths. Inaddition, the added switching capability of the switching network 710maintains the option of bypass signal paths (through the IC_Sx seriesswitches) that are isolated from the target circuit 706.

As is the case with the RF signal switch circuit 300 of FIG. 3 , inalternative embodiments of the RF signal switch circuit 700, each of theRF input terminals RF₁-RF_(N) may have one or more sets of in-pathconnector series switch IC_S_(x), and corresponding isolation shuntswitches Sh_(I) connected to parallel in-circuit paths. Such aconfiguration would, for example, allow multiple antennas to beselectively coupled to multiple target circuits without increasing thenumber of series switches to any one target circuit. In otherembodiments, multiple target circuits 706 may be included, withconcomitant replication of the first switch path 712 of the switchingnetwork 710 to provide corresponding connections to the RF₀ port.

All of the switches described above for FIG. 7 may be controlled byexternal switching circuitry (not shown) of conventional design to seteither open states or closed states for the switches. One or more of theswitches shown in FIGS. 3 and 7 may be of any type, but are beneficiallyfabricated as field effect transistors (FETs), and particularly asMOSFETs, on an integrated circuit.

Other circuitry may be included in the triple-mode RF signal switchcircuit 700 as desired or needed for particular applications. Forexample, in some applications, it may be desirable to insert a fixedattenuation circuit in line with the bypass signal path to provide aminimum amount of attenuation to applied RF signal. As another example,if even higher isolation of the target circuit 706 is desired, some orall of the switches coupled to the target circuit 706 may be replaced bya “T” type series/shunt/series circuit bypass switch configuration ofthe type shown in FIG. 5 .

Methods

Another aspect of the invention includes a method for switching RFsignals, including:

-   -   a. providing at least one RF input port having a shunt switch, a        bypass switch, and an in-path connector switch;    -   b. coupling each in-path connector switch to an in-circuit path,        the in-circuit path being configured to be coupled to an input        of a target circuit;    -   c. coupling each bypass switch to a switch output port;    -   d. coupling each shunt switch to circuit ground;    -   e. coupling an isolation shunt switch to the in-circuit path;    -   f. providing a switch return path, the switch return path being        configured to be coupled to an output of the target circuit;    -   g. coupling an output connector shunt switch to the switch        return path; and    -   h. coupling an output connector switch to the switch return path        and to the switch output port.

Yet another aspect of the invention encompasses the first method setforth above, further including configuring an in-circuit mode for aselected RF input port by:

-   -   a. setting the shunt switch and bypass switch for the selected        RF input port to an open state, setting the in-path connector        switch for the selected RF input port to a closed state, setting        the isolation shunt switch to an open state, setting the output        connector shunt switch to an open state, and setting the output        connector switch to a closed state; and    -   b. for each other RF input port, setting the respective in-path        connector switch and bypass switch to an open state, and setting        the respective shunt switch to a closed state.

Still another aspect of the invention encompasses the first method setforth above, further including configuring a bypass mode for a selectedRF input port by:

-   -   a. setting the shunt switch and the in-path connector switch for        the selected RF input port to an open state, setting the bypass        switch for the selected RF input port to a closed state, setting        the isolation shunt switch to a closed state, setting the output        connector shunt switch to a closed state, and setting the output        connector switch to an open state; and    -   b. for each other RF input port, setting the respective in-path        connector switch and bypass switch to an open state, and setting        the respective shunt switch to a closed state.

Another aspect of the above methods is configuring each bypass switch asa “T” type series/shunt/series circuit, and (a) for an active signalpath in the bypass mode, setting a first series switch and a secondseries switch to a closed state, and setting a shunt switch to an openstate; and (b) for an active signal path in the in-circuit mode and forinactive signal paths in either mode, setting the first series switchand the second series switch to an open state, and setting the shuntswitch to a closed state.

Still another aspect of the invention is a method of switching RFsignals, including providing at least one first type RF signal port,each first type RF signal port having a first shunt switch coupled tothe first type RF signal port and configured to selectively couple thefirst type RF signal port to circuit ground, a first series switchcoupled between the first type RF signal port and configured to becoupled to at least one corresponding target circuit, and at least oneset of second series switches coupled to the first type RF signal port;coupling at least one first circuit path to a corresponding second shuntswitch and coupled to a corresponding one set of second series switches,each first circuit path being configured to be coupled to at least onesignal function circuit; providing at least one second circuit pathconfigured to be coupled to the at least one signal function circuit,and being coupled to a corresponding third shunt switch; coupling atleast one third series switch to a corresponding one second circuit pathand to at least one first series switch; providing at least one secondtype RF signal port; and coupling a switching network to the at leastone second type RF signal port, the switching network including at leastone first switch path each having a series switch coupled to at leastone second type RF signal port and configured to be coupled to onecorresponding target circuit, and a shunt switch coupled to a nodebetween such series switch and such corresponding target circuit andconfigured to selectively couple that node to circuit ground, and atleast one second switch path each having a first series switch coupledto the at least one second type RF signal port, a second series switchcoupled to the first series switch and to at least one second circuitpath, and a shunt switch coupled to a node between the first and secondseries switches and configured to selectively couple that node tocircuit ground.

The method immediately above may further include or be characterized byone or more of the following:

-   a. configuring a bypass mode for a selected first type RF signal    port such that an applied RF signal passes between the selected    first type RF signal port and at least one corresponding second type    RF signal port through a corresponding second switch path of the    switching network, a corresponding second circuit path, a    corresponding first circuit path, and a corresponding second series    switch of the selected first type RF signal port, such that each    target circuit is isolated from the selected first type RF signal    port and the at least one corresponding second type RF signal port;-   b. configuring a bypass mode for a selected first type RF signal    port, including closing at least one second series switch for the    selected first type RF signal port, closing the first and second    series switch of a corresponding second switch path of the switching    network, opening all other series switches, opening the first shunt    switch coupled to the selected first type RF signal part, opening    the shunt switch coupled to each pair of closed first and second    series switches of the corresponding second switch path of the    switching network, opening the third shunt switch of the second    circuit path corresponding to the pair of closed first and second    series switches of the second switch path of the switching network,    and closing all other shunt switches;-   c. configuring a low loss mode for a selected first type RF signal    port such that the selected first type RF signal port is coupled to    at least one corresponding target circuit through only the first    connector switch for the selected first type RF signal port and    through no other switch;-   d. configuring a low loss mode for a selected first type RF signal    port, including closing the first series switch for the selected    first type RF signal port, closing the series switch of at least one    first switch path of the switch network, opening all other series    switches, opening the first shunt switch for the selected first type    RF signal port, opening the shunt switch corresponding to the closed    series switch of the at least one first switch path of the switch    network, and closing all other shunt switches;-   e. configuring a signal function mode for a selected first type RF    signal port such that the selected first type RF signal port is    coupled to at least one corresponding target circuit through at    least one signal function circuit;-   f. configuring a signal function mode for a selected first type RF    signal port, including closing at least one second series switch for    the selected first type RF signal port, closing the third series    switch of at least one second circuit path coupled to the closed    second series switch for the selected first type RF signal port,    closing the series switch of at least one first switch path of the    switch network, opening all other series switches, opening the first    shunt switch coupled to the selected first type RF signal part;    opening the shunt switch corresponding to the closed series switch    of the at least one first switch path of the switch network, opening    the third shunt switch corresponding to each closed third series    switch, and closing all other shunt switches;-   g. coupling a signal function circuit between one first circuit path    and one second circuit path, for selectively altering the phase    and/or amplitude of an RF signal conveyed between the one circuit    path and the one second circuit path;-   h. coupling at least one target circuit between the series switch of    at least one corresponding first switch path of the switching    network and the first series switch of at least one first type RF    signal port;-   i. wherein at least one target circuit includes a low noise    amplifier and/or an impedance matching network;-   j. coupling at least one second signal function circuit between a    corresponding target circuit and the series switch of at least one    corresponding first switch path of the switching network; and/or-   k. implementing each switch with at least one field effect    transistor.

Uses

Circuits and devices in accordance with the present invention may beused alone or in combination with other components, circuits, anddevices. Embodiments of the present invention may be fabricated asintegrated circuits (ICs), which may be encased in IC packages and/or ormodules for ease of handling, manufacture, and/or improved performance.

Embodiments of the present invention are useful in a wide variety oflarger radio frequency (RF) circuits and systems for performing a rangeof functions, including (but not limited to) impedance matchingcircuits, RF power amplifiers (e.g., scalable periphery tunable matchingpower amplifiers and Doherty amplifiers), RF low-noise amplifiers(LNAs), phase shifters, attenuators, RF switches, etc. Such functionsare useful in a variety of applications, such as radar systems(including phased array and automotive radar systems), radio systems(including cellular radio systems), and test equipment. Such circuitsmay be useful in systems operating over some or all of the RF range(e.g., from around 20 kHz to about 300 GHz).

Radio system usage includes wireless RF systems (including basestations, relay stations, and hand-held transceivers) that use varioustechnologies and protocols, including various types of orthogonalfrequency-division multiplexing (“ODFM”), quadrature amplitudemodulation (“QAM”), Code Division Multiple Access (“CDMA”), Wide BandCode Division Multiple Access (“W-CDMA”), Worldwide Interoperability forMicrowave Access (“WIMAX”), Global System for Mobile Communications(“GSM”), Enhanced Data Rates for GSM Evolution (EDGE), Long TermEvolution (“LTE”), as well as other radio communication standards andprotocols.

Fabrication Technologies & Options

The term “MOSFET”, as used in this disclosure, means any field effecttransistor (FET) with an insulated gate and comprising a metal ormetal-like, insulator, and semiconductor structure. The terms “metal” or“metal-like” include at least one electrically conductive material (suchas aluminum, copper, or other metal, or highly doped polysilicon,graphene, or other electrical conductor), “insulator” includes at leastone insulating material (such as silicon oxide or other dielectricmaterial), and “semiconductor” includes at least one semiconductormaterial.

As should be readily apparent to one of ordinary skill in the art,various embodiments of the invention can be implemented to meet a widevariety of specifications. Unless otherwise noted above, selection ofsuitable component values is a matter of design choice and variousembodiments of the invention may be implemented in any suitable ICtechnology (including but not limited to MOSFET structures), or inhybrid or discrete circuit forms. Integrated circuit embodiments may befabricated using any suitable substrates and processes, including butnot limited to standard bulk silicon, silicon-on-insulator (SOI), andsilicon-on-sapphire (SOS). Unless otherwise noted above, the inventionmay be implemented in other transistor technologies such as bipolar,GaAs HBT, GaN HEMT, GaAs pHEMT, and MESFET technologies. However, theinventive concepts described above are particularly useful with anSOI-based fabrication process (including SOS), and with fabricationprocesses having similar characteristics. Fabrication in CMOS on SOI orSOS processes enables circuits with low power consumption, the abilityto withstand high power signals during operation due to FET stacking,good linearity, and high frequency operation (i.e., radio frequencies upto and exceeding 50 GHz). Monolithic IC implementation is particularlyuseful since parasitic capacitances generally can be kept low (or at aminimum, kept uniform across all units, permitting them to becompensated) by careful design.

Voltage levels may be adjusted or voltage and/or logic signal polaritiesreversed depending on a particular specification and/or implementingtechnology (e.g., NMOS, PMOS, or CMOS, and enhancement mode or depletionmode transistor devices). Component voltage, current, and power handlingcapabilities may be adapted as needed, for example, by adjusting devicesizes, serially “stacking” components (particularly FETs) to withstandgreater voltages, and/or using multiple components in parallel to handlegreater currents. Additional circuit components may be added to enhancethe capabilities of the disclosed circuits and/or to provide additionalfunctionality without significantly altering the functionality of thedisclosed circuits.

CONCLUSION

A number of embodiments of the invention have been described. It is tobe understood that various modifications may be made without departingfrom the spirit and scope of the invention. For example, some of thesteps described above may be order independent, and thus can beperformed in an order different from that described. Further, some ofthe steps described above may be optional. Various activities describedwith respect to the methods identified above can be executed inrepetitive, serial, or parallel fashion.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the following claims, and that other embodiments arewithin the scope of the claims. (Note that the parenthetical labels forclaim elements are for ease of referring to such elements, and do not inthemselves indicate a particular required ordering or enumeration ofelements; further, such labels may be reused in dependent claims asreferences to additional elements without being regarded as starting aconflicting labeling sequence).

What is claimed is:
 1. A radio frequency (RF) signal switch including:(a) a plurality of switch groups, each switch group configured toselectively couple, independently of any other switch group, acorresponding RF signal port to one of a common signal path, acorresponding circuit ground port, or a common connection port coupledto all of the switch groups; (b) an RF switch port couplable, directlyor indirectly, to the common signal path or the common connection port;and (c) a shunt switch device coupled to the common connection port ofthe switch groups and configured to selectively isolate the commonconnection port from circuitry coupled between the common connectionport and the RF switch port.
 2. The invention of claim 1, wherein in anin-circuit mode, the RF signal switch may be configured such that asignal applied to the RF signal port of a selected switch group passesthrough a target circuit coupled between the common connection port ofthe switch groups and the RF switch port.
 3. The invention of claim 1,wherein in a bypass mode, the RF signal switch may be configured suchthat a signal applied to the RF signal port of a selected switch grouppasses to the RF switch port through the common signal path.
 4. Theinvention of claim 1, wherein the RF signal switch in a bypass mode maybe configured such that a signal applied to the RF signal port of aselected switch group passes to the RF switch port through the commonconnection port of the switch groups.
 5. The invention of claim 1,wherein the RF signal switch in a first in-circuit mode may beconfigured such that a signal applied to the RF signal port of aselected switch group passes to the RF switch port through a targetcircuit.
 6. The invention of claim 1, wherein the RF signal switch in asecond in-circuit mode may be configured such that a signal applied tothe RF signal port of a selected switch group passes to the RF switchport through a signal function circuit and through a target circuit. 7.A radio frequency (RF) signal switch including: (a) a plurality ofswitch groups, each switch group configured to selectively couple,without any intervening switches, a corresponding RF signal port to oneof a common signal path, a corresponding circuit ground port, or acommon connection port coupled to all of the switch groups; (b) an RFswitch port couplable, directly or indirectly, to the common signal pathor the common connection port; and (c) a shunt switch device coupled tothe common connection port of the switch groups and configured toselectively isolate the common connection port from circuitry coupledbetween the common connection port and the RF switch port.
 8. Theinvention of claim 7, wherein in an in-circuit mode, the RF signalswitch may be configured such that a signal applied to the RF signalport of a selected switch group passes through a target circuit coupledbetween the common connection port of the switch groups and the RFswitch port.
 9. The invention of claim 7, wherein in a bypass mode, theRF signal switch may be configured such that a signal applied to the RFsignal port of a selected switch group passes to the RF switch portthrough the common signal path.
 10. The invention of claim 7, wherein ina bypass mode, the RF signal switch may be configured such that a signalapplied to the RF signal port of a selected switch group passes to theRF switch port through only one switch within the switch group, the oneswitch corresponding to the selected RF signal port.
 11. A radiofrequency (RF) signal switch including: (a) a plurality of switchgroups, each switch group configured to selectively couple acorresponding RF signal port to one of a common signal path, acorresponding circuit ground port, or a common connection port coupledto all of the switch groups; (b) an RF switch port; (c) a shunt switchdevice coupled to the common connection port of the switch groups andconfigured to selectively isolate the common connection port fromcircuitry coupled between the common connection port and the RF switchport; and (d) a switching network coupled to the RF switch port andconfigured to be selectively coupled to a target circuit or to thecommon connection port of the switch groups or to the common signalpath.
 12. The invention of claim 11, wherein the RF signal switch in abypass mode may be configured such that a signal applied to the RFsignal port of a selected switch group passes to the RF switch portthrough the common connection port of the switch groups and theswitching network.
 13. The invention of claim 11, further including atarget circuit coupled between the common signal path and the RF switchport.
 14. The invention of claim 11, wherein the RF signal switch in afirst in-circuit mode may be configured such that a signal applied tothe RF signal port of a selected switch group passes to the RF switchport through a target circuit.
 15. The invention of claim 11, whereinthe RF signal switch in a second in-circuit mode may be configured suchthat a signal applied to the RF signal port of a selected switch grouppasses to the RF switch port through a signal function circuit and atarget circuit.